The refrigeration cycle is a critical component of HVAC systems and is governed by the principles of thermodynamics. If P, V and T represent the pressure, volume and temperature of the gaseous system, respectively, at any stage, then the correct equation representing the process is (a) TV 2/5 = constant (b) VP 5/3 = constant (c) TP-2/5 = constant (d) PT 2/5 = constant. This will not occur within a properly working refrigeration system, but can occur when: A pressure-relief valve discharges if it is venting vapor R744 Evaporator: this is a heat exchanger similar to a radiator when used with air (finned coil) or more compact when used with water (plate heat exchanger, tube bundle); it exchanges energy by conduction between the refrigerant that evaporates, changing state from liquid to gas, and the surrounding air (or water) that's. Lets use water for the following example: At sea level water boils at 212 degrees Fahrenheit. subcooled while superheating gaseous refrigerant (pro-cess a→b). It is a compression process, whose aim is to raise the refrigerant pressure, as it flows from an evaporator. A significant amount of energy is required to induce changes of state, whether it be evaporation or condensation. Now that we know these principles, we can talk about how the refrigeration cycle works in HVAC. Low-pressure liquid that is leaving the metering device is boiling at saturated pressure-temperature. Because the pressure drops so rapidly at the expansion device, the refrigerant turns into a combination of a cold liquid and vapor. If we take an 8oz cup of 150 degree coffee and mix it with an 8oz cup of 50 degree iced coffee, we would create a 16oz coffee with a temperature of 100 degrees. The result is low-pressure Freon gas. What is the primary function of all metering devices? The compressor is often referred to as the heart of the refrigeration system. Now at a low-pressure, the refrigerant moves to the evaporator, which absorbs heat from the outside air, and changes the liquid back to a gas. Similarly, you may ask, what is the state of the refrigerant as it leaves the metering device? Like the condenser coil, the evaporator coil also winds through the evaporator to maximize heat transfer from the refrigerant to the air. Lower pressures make it easier for a liquid to boil, and higher pressures make it more difficult. This happens when warm outdoor air is blown across the condenser coil that is filled with hot, gaseous refrigerant. By the time the refrigerant is discharged, it is fully pressurized. A low pressure gaseous refrigerant bypass to the compressor may also be provided for permitting a portion of the compressed refrigerant in the compressor to be discharged, thereby reducing the danger of overheating of the compressor. An HVACR compressor is a refrigerant gas pump in which the evaporator supplies gaseous refrigerant at a low pressure and increases it to a greater pressure. The compressor compresses the refrigerant in the gaseous … Keep in mind these core principles of the refrigeration cycle will always remain the same, even when we get into more complex HVAC systems like chillers. The process of a refrigerant changing its state (from a liquid to a vapor) in the metering device is called flash gas. Before we dive in, let’s get an understanding of four key concepts: This is the amount of heat required to turn a liquid into a gas. Heat transfers from the air to the refrigerant, which cools the air directly before it is vented to the space. This causes a temperature increase. This allows heat to transfer from the refrigerant to the cooler outdoor air, where the excess heat is rejected to the atmosphere. 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